The technology of capacitance-type material level indication has been employed in a number of applications, including measurement and display of fuel level in automotive and other vehicles. In general, systems of this character seek to measure and display material level as a function of the effective capacitance of material between a pair of measurement probes, or between a measurement probe and the vessel wall, which capacitance varies with material level. A general problem in application of such technology to fuel level measurement lies in the fact that many fuels exhibit both electrically conductive and electrically capacitive characteristics. This problem is compounded in vehicles which can employ fuels of differing conductivity. Gasohol containing 10% ethyl alcohol, for example, may possess a conductivity which is ten times that of regular unleaded gasoline. It is desirable to provide a level indicating system which not only compensates for fuel conductivity, but also compensates for differing conductivities in the types of fuels which can be employed.
A general object of the present invention is to provide a system of the described character which is inexpensive in manufacture, and is reliable in operation over a substantial operating lifetime and in a variety of operating environments.
Another and more specific object of the invention is to provide a material level indicating system of the described character which finds particular application in conjunction with electrically conductive materials such as gasoline.
A yet more specific object of the invention is to provide a level indicating system for conductive materials such as gasoline which automatically compensates for material conductivity, and which is adapted to accommodate materials of varying conductivity, such as gasoline containing a varying amounts of alcohol.